Dungeon ni Deai o Motomeru no wa Machigatte Iru Darou ka - Vol 1 Chapter 0: Prologue

A 13-year-old deaf teenager living in the 21st century suddenly found himself as a young boy in Japan during the early 1900s. With two World Wars, two nuclear bombs, Hitler and many other disasters awaiting his future, he thought things couldn't get worse.Except it did.He found out later on that he had actually reincarnated into the world of Demon Slayer where man-eating demons ruled the night. He thought things couldn't get worse.Except it did.But hey! At least he had unparalleled talent, incredibly special eyes and future knowledge.How will the story of Demon Slayer change with the addition of this unique character? Will so many still die if the Hashiras had one more pillar in the final battle?Or will the story end on a much happier note?

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When an S-class elite assassin-raised captain of a special ops suicide squad comes home from a high-stakes Africa mission, he finds himself offered something that could potentially set him up for life- a curious assignment that he could use to finally exit his days of war and slaughter.

Then placed into a high-school setting, Lin Yi is tasked by the chairman of a top-tier multi-billion company with bodyguard duty for non-other than his own daughter, a certain little Miss of said high-school.

His enemies, once ranging from drug lords, mafia bosses, political figures, and national leaders, are soon replaced with spoiled kids who happen to have rich papas and mamas, and Lin Yi finds his intense expertise and high-threat skillset misused, and very underwhelmed…

But he does get a harem cast as diverse as his old enemies, so Lin Yi decides that, for the sake of messing around with girls as an invincible entity in a down-leveled environment, leaving his bloody and death-filled war days behind is something he’d definitely want to strive for.

- Description from Novelupdates

Li Ke Lin (also Li Colin), a Chinese office worker, woke up to find himself suddenly no longer Li Ke Lin but instead Colin Lee, son of multi-billionaire in America. Having taken over the body of Colin Lee and carefully imitated his manners and bearings, his next goal is to inherit his father’s wealth. However, when his father lists the condition of marrying a woman who feels repulsed by Colin Lee’s (not Li Colin’s) dalliances, and whose very nature is the complete opposite of Colin Lee (not Li Colin), what must he do to gain her affection?!